1. Field of the Invention
This invention relates to cementitious mixtures and their use, and more particularly, but without limitation, to lightweight or insulating cementitious mixtures, structures formed therefrom and methods of use thereof.
2. Description of the Prior Art
Lightweight materials with good thermal insulating characteristics are desirable for use in building panels, and in particular, tilt-up wall panels. Use of lightweight aggregates in concrete have been used for such purposes, and the American Society for Testing and Materials has published ASTM Specification C322 entitled "Lightweight Aggregates For Insulating Concrete". This specification covers lightweight aggregates intended for use in concrete not exposed to weather, in which the prime consideration is the thermal insulating property of the resulting concrete. One problem with such materials is that the insulating aggregate greatly reduces the compressive strength of the concrete.
Specifically, vermiculite has been used in cementitious mixtures. For example, ASTM Specification C322, Group I covers one of two general types of lightweight aggregates, particularly aggregates prepared by expanding products such as perlite or vermiculite. The vermiculite in such aggregates provides the thermal insulating characteristics and is also used specifically because it will readily absorb and hold liquid water by capillary penetration. A material purporting to conform with ASTM Spec C332, Group I is sold under the name "Zonolite Insulating Concrete" by W. R. Grace & Company.
The strength of lightweight insulating concretes is not sufficient to be suitable for exterior surfaces. Also, the vermiculite in such materials will still absorb water which is unsatisfactory for exterior surfaces.
The use of polypropylene fibers to reinforce cementitious mixtures is disclosed in U.S. Pat. No. 3,591,395 to Zonsveld et al. Such fibers are sold under the name of "Forta Fibre" by Forta Fibre, Inc.